Corrosion-inhibited liquid fertilizer



United States Patent 25,394 CORROSION-INHIBITED LIQUID FERTILIZERCOMPOSITIONS Carl Robert Martinson, Belleville, Ill., assignor toMonsanto Chemical Company, St. Louis, Mo., a corporatlou of Delaware NoDrawing. Original No. 3,024,099, dated Mar. 6, 1962, Ser. No. 660,038,May 20, 1957. Application for reissue Sept. 26, 1962, Ser. No. 228,214

This invention relates to improved liquid fertilizer compositions whichare characterized by a material reduction in the corrosion of storagecontainers and application equipment. More specifically this inventionrelates to corrosion-inhibited liquid fertilizer compositions which aresuitably used in aluminum equipment.

An early source of nitrogen in agricultural application was the use ofammonium nitrate solutions. The ammonium nitrate solutions weregenerally held in aluminum storage tanks and dispensed in the field withaluminum equipment. Accordingly, the industry has a considerable presentinvestment in aluminum storage vessels and application equipment. Inrecent years there has been a Re. 25,394 Reissuecl June 11, 1963 "icepreferred suitable fiuosilicates are sodium fluosilicate, ammoniumfluosilicate and potassium fiuosilicate.

The substantially neutral liquid fertilizer compositions are generallyformulated by various mixtures of monoammonium phosphate, diammoniumphosphate, ammonium nitrate, ammonium sulfate, urea, potassium chloride,potassium nitrate, monopotassium phosphate, dipotassium phosphate andthe like or by the use of anhydrous ammonia, aqua ammonia, phosphoricacid, potassium hydroxide and the like to directly produce asubstantially neutral salt solution. Thus the neutral liquid fertilizersolutions can be a solution of ammonium phosphate or ammonium phosphateto which has been added ammonium nitrate, urea, potassium chloride andthe like to form a variety of N-P or NPK liquid fertilizers. The pH ofthe liquid fertilizer composition preferably ranges from about 6 toabout 8.

As is well known, fertilizer compositions are conventionally labeled interms of the principal nutrient com.- ponents therein, i.e. nitrogen,phosphorus and potassium, wherein phosphorus and potassium are given interms of P 0 and K 0, respectively, and the N-PK designation hereinaboveand hereinafter employed will be understood in these terms.

Various illustrative neutral liquid fertilizer compositions are shown inthe following table wherein the various components are indicated inparts by weight.

Phos- M ono- Diam- Ammo- Ammophorlc ammomonlum Potas- Potas- No. lN-P-kAmmonia mum Ilium Urea acid niurn phossium sium lTVuter nitrate sulfate(75%) phosphate chloride nitrate phate growing demand for liquidfertilizers generally, i.e. fertilizer compositions which also contain P0 with or without K 0 to provide a complete liquid formulation. Howeverit was found that the presence of liquid fertilizer compositionscontaining P 0 caused excessive corrosion to the aluminum equipmentwhich was then in wide use.

It is the principal object of this invention to provide a substantiallyneutral liquid fertilizer composition con taining P 0 which can bestored and dispensed with aluminum equipment. Another object of thisinvention is to provide a substantially neutral liquid fertilizercomposition containing P 0 which is characterized by a low rate ofcorrosion when employed with aluminum equipment. Other objects will beapparent from the following disclosure.

It has now been found that from about 200 up to about 500 ppm. offluoride as a soluble fiuosilicate when present in substantially neutralliquid fertilizer compositions containing the phosphate nutrient, i.e.the orthophosphate ion, provides a liquid fertilizer composition whichcan be employed in aluminum equipment. The

The pH of the above formulations as a l to 10 dilution with water willvary between about 6 to about 8 and most will vary between about 6.5 toabout 7.5.

The subject liquid fertilizer compositions can also contain minoramounts of surfactants to facilitate the assimilation of the nutrientcomposition by the plant, minor amounts of essential trace elements inavailable form and the like. The desired liquid fertilizer compositioncan be formulated batchwise or by a continuous process as will bereadily understood by those skilled in the art.

The following examples are illustrative of the instant invention.

EXAMPLE 1 Since the high phosphate content liquid fertilizer compositionwas found to cause the most severe corrosion rate of the variousformulations, the 8-24-0 composition was selected such that thefollowing evaluation results would generally exemplify the most drasticcorrosive effects which might be met in the field.

A liquid fertilizer composition (8-24-0) was prepared by dissolving 1.07parts by weight of monoarnmonium phosphate and 328.1 parts by weight ofdiammonium phosphate in 564.9 parts by Weight of water. Similar"compositions were prepared which contained varying amounts of fluorine,as sodium fluosilicate, as a corrosion inhibitor in the said liquidfertilizer composition. The corrosion rates of the liquid fertilizercompositions on 350 aluminum at 140 F. are shown in the following table:

I.p.rn, fln- Rate oi eor- N0. urine as rosiun (mils/ N mSiFn year) Itwas also found that the presence of minor amounts of the sodiumfluosilicate was beneficial even in the less corrosive liquid fertilizercompositions. Thus a 3-9-9 formulation was prepared by dissolving 4pounds of monoammonium phosphate, 12.3 pounds of diammonium phosphateand 14.5 of potassium chloride in 69.2 pounds of water per 100 pounds ofliquid fertilizer composition and a 10-5-5 formulation was prepared bydissolving 2.2 pounds of monoammonium phosphate, 6.8 pounds ofdiammonium phosphate, 24 pounds of ammonium nitrate and 8.1 pounds ofpotassium chloride in 58.9 pounds of water per 100 pounds of liquidfertilizer composition. When the aforesaid liquid fertilizercompositions were inhibited by the addition thereto of about 250 p.p.m.of fluorine as sodium fluosilicate and the rate of corrosion evaluatedin the presence of 380 aluminum at about 140 F., it was found that thecorrosion rate of each of said fertilizer compositions was reduced tosubstantially zero.

Qualitative and quantitative evaluation of the liquid fertilizercompositions containing up to 500 p.p.m. of fluorine as sodiumfiuosilicate conclusively demonstrated that the inhibited fertilizercompositions produced no phytotoxic effect on the germination or growthof radish, cucumber, tomato and rye grass seeds.

The aforesaid a plants do not have particularly hardy seedlings,accordingly, it can be reasonably concluded that since the inhibitedformulation exhibits no deleterious effects to these seedlings, it canbe safely used with any seedlings and/or plants. However, it isrecommended that concentrations greater than 500 p.p.m. of fluorineshould be avoided as such solutions may be phytotoxic to some plants.

What is claimed is:

I. A process for inhibiting the corrosion of aluminum by aqueous liquidfertilizer compositions having a pH between about 6 and about 8 andcontaining an inorganic orthophosphate salt selected from the groupconsisting of monoammom'um orthophosphate, diammonium orthophosphate,monopotassium orthophosphate and dipotassium orthophosphate, saidprocess comprising the incorporation therein of an eflective corrosioninhibiting amount of a soluble fluosilicate compound selected from thegroup consisting of sodium fluosilicate, potassium fluosilicate andammonium fluosilicate.

2. A process as in claim 1, wherein said fluosilicate compound is sodiumfluosilicate.

3 [1]. A method of inhibiting the corrosion of aluminum equipment byaqueous, liquid fertilizer compositions having a pH between about 6 andabout 8 and containing an inorganic orthophosphate salt selected fromthe group consisting of monoammonium orthophosphate, diamrnoniumorthophosphate, monopotassium orthophosphate, and dipotassiumorthophosphate, said method comprising the incorporation therein of fromabout 200 to about 500 p.p.m. of fluorine as a soluble fluosilicatecompound selected from the group consisting of sodium fluosilicate,potassium fluosilicate, and ammonium fluosilicate.

4 [2]. The method of claim 3 [1], wherein about 500 p.p.m. fluorine assodium fluosilicate is employed.

References Cited in the file of this patent or the origmal patent UNITEDSTATES PATENTS 2,028,343 Michel Jan. 21, 1936 2,238,651 Keenan Apr. 15,1941 2,586,709 Phillips Feb. 19, 1952 2,719,781 Hesch Oct. 4, 19552,732,290 Vana et a1 Jan. 24, 1956 2,739,886 Facer Mar. 27, 19562,778,712 Caldwell Jan. 22, 1957 FOREIGN PATENTS 736,215 Great BritainSept. 7, 1955

